The present invention relates to imaging inspection systems and techniques. More specifically, the present invention relates to a novel method and apparatus for imaging obscured areas of a test object.
In the field of automatic inspection devices, systems are known that are capable of providing diagnostic information, whether qualitative or quantitative, about a region of interest. In certain applications, such as the inspection of printed circuit boards ("PCBs"), the region of interest may lie in a particular plane within or on the surface of an object being inspected. It is therefore desirable to extract the diagnostic information from the plane containing the region of interest while ignoring information produced by artifacts or substances lying outside the region of interest. The present invention relates to systems and techniques used to produce a representation of a two-dimensional plane passing through a three-dimensional test object.
An automatic inspection device that is capable of providing diagnostic information from the plane containing the region of interest within or on the surface of the test object is shown, for example, in U.S. Pat. No. 5,097,492 issued to Baker et al. Baker shows an automated laminography system for the inspection of electronics. An electron beam within an x-ray source is deflected to scan a circular pattern on a target anode. An x-ray detector is rotated in synchronization with the deflection of the electron beam to intercept x-rays transmitted through the region of interest within the test object. The inspection device produces a laminographic cross-sectional image.
A disadvantage of the Baker device is that the detector is rotated in synchronization with the steering of the electron beam, requiring precise mechanical control of the detector position as well as increased mechanical complexity. Formation of a high resolution laminographic cross-sectional image depends upon the precise alignment and synchronization of the circular motions of the x-ray source and detector. A further disadvantage of the Baker device is that blurred information may mask diagnostic information, particularly where x-ray opaque substances are located above or below the region of interest. A still further disadvantage of the Baker device is that the circular acquisition geometry of the source and detector may not provide a sufficient representation of the region of interest for all PCBs.
Accordingly, it would be desirable to have an improved method and apparatus for imaging obscured devices.